The drilling of boreholes deep into the bosom of the earth require special equipment and technology. The conventional rotary drill bit, when extended 30,000 feet into the earth, requires careful consideration of the drill string because ordinary drill pipe can hardly support itself beyond this tremendous depth. Moreover, the massive drawworks required for rotating and manipulating a 30,000 foot conventional tool string is awesome to those not highly skilled in the art.
The drilling of extremely deep boreholes requires that particular attention be paid to the hydrostatic head effected within the annulus for the reason that exceptionally high pressures can be encountered as the borehole is sunk through unknown geological formations.
In sinking extremely deep boreholes, it is therefore desirable to have made available a very light weight, durable drill string. On the other hand, it is necessary that the borehole forming tool string have adequate weight effected on the bit thereof so that the bit can be made to properly engage the borehole bottom with sufficient force to efficiently remove cuttings therefrom. Therefore, it is advantageous that a tool string for deep holes have as much weight as possible consigned to the area near the drill bit motor, while at the same time the structural integrity of the drill string enables proper and safe manipulation of the entire tool string.
Reciprocatory drill bits have many advantages over a rotary type bit, and vice versa. The reciprocatory or vibrating bit is still held in high esteem by some drillers for penetrating very hard formations. There are many advantages realized with a reciprocatory drill bit when making a deep hole, especially when the bit motor is located downhole adjacent the bit. Examples of reciprocatory bits and motors are set forth in U.S. Pat. Nos. 2,949,850 to Heath; 2,340,738 to Dilly; and 1,062,050 to Stewart.
There are many problems to be overcome in order to conduct a source of power from the surface of the earth down to a motor device located downhole adjacent to the bit and solutions thereto are the subject of several patented inventions, as for example:
Godbey U.S Pat. No. 4,012,092; Hull et al U.S. Pat. No. 2,795,367; Garrett U.S. Pat. No. 4,436,118; and Cunningham U.S. Pat. No. 4,445,734.
In drilling deep holes, it is desirable to maintain the hole deviation to a minimum by the provision of an apparatus which senses the direction of hole deviation and changes the direction of penetration of the bit to maintain the hole axis aligned along a vertical axis. Jeter Re 29,526 is an example of the prior art. Other prior art patents related to the present combination are:
______________________________________ U.S. Pat. No. issued to on ______________________________________ 2,858,180 Wise October 20, 1958 2,868,507 Scott January 15, 1959 3,043,381 McNeely Jr. July 10, 1962 3,811,519 Driver May 21, 1974 3,903,974 Cullen September 9, 1975 3,139,146 Bodine June 30, 1964 4,354,561 Logan October 19, 1982 ______________________________________
The present invention sets forth a new combination of elements assembled in a manner to provide a novel drill string apparatus by which a deep hole can be achieved.
There are numerous other patents directed to concentric drill pipe wherein drilling fluid flows to and from the bit along isolated annular flow paths. These patents relate to the "concore" method of drilling and are considered of interest, but do not comprehend nor solve all of the problems involved herein.